Cerium-based abrasive abrasive and abrasive material slurry, and method for producing cerium based abrasive material

ABSTRACT

There is provided a cerium-based abrasive containing cerium oxide as a main component, in which the abrasive particles composing the abrasive are coated with a coating layer containing at least either one of a silicon component of silicon or a silicon compound and an aluminum component of aluminum or an aluminum compound. The cerium-based abrasive can be produced by wet-dispersing the cerium-based abrasive in a dispersion medium to obtain a slurry and carrying out surface treatment by adding a treatment solution containing at least either one of the silicon compound and the aluminum compound to the slurry. Further, the cerium-based abrasive can be produced by carrying out surface treatment by adding a treatment solution containing at least either one of the silicon compound and the aluminum compound to the slurry during the pulverization step or after the pulverization step in the conventional cerium-based abrasive production process and after that roasting and classifying the obtained cerium-based abrasive.

FIELD OF THE INVENTION

[0001] The present invention relates to a cerium-based abrasive. Moreparticularly, the invention relates to a cerium-based abrasive with highfluidity and dispersibility and excellent in polishing properties.

BACKGROUND OF THE ART

[0002] The range of the use of a cerium-based abrasive containingcerium-based particles as a main component has rapidly been increasingowing to the excellent polishing effects and the functions of a varietyof additives added to the abrasive. Today, it is employed not only for aconventional purpose of polishing optical glass but for the fields ofpolishing glass for a liquid crystal, glass for a magnetic recordingmedium such as hard disks, and fabricating an electronic circuit such asLSI.

[0003] The cerium-based abrasive has generally been produced by thefollowing method. That is, raw materials are made to be a slurry,wet-pulverized, treated with a mineral acid as required, and thensubjected to chemical treatment with hydrofluoric acid, ammoniumfluoride, and the like. The obtained slurry is filtered, dried, androasted, the resulting particle is then pulverized and classified toobtain an abrasive particle having a desired particle diameter. Rareearth raw materials such as rare earth carbonates, rare earthhydroxides, rare earth oxalates, or rare earth oxides obtained by firingthese compounds are used as the raw materials of the cerium-basedabrasive. These rare earth raw materials have been produced generally byremoving some rare earth metals (Nd, Pr, etc.) and radioactive elementsfrom bastnasite-based rare earth raw materials or cerium-containing rareearth raw materials by a well-known chemical treatment.

[0004] The cerium-based abrasive is assumed to have a high polishingspeed and further is required to produce a polished face with excellentspecular properties. Although these properties are required not only forcerium-based one but also for an abrasive generally, the cerium-basedone is required to be excellent in the polishing properties and to beimproved in other properties as well.

[0005] For example, the cerium-based abrasive is generally dispersed ina dispersion medium such as water and mixed with a dispersant, a pHadjusting agent, and the like, as required, and then supplied to apolishing apparatus. Consequently, it is important for a dried abrasiveparticle powder to be quickly dispersed in water and to become an evenslurry.

[0006] Further, the adhesive property of the abrasive particles to thesurface of an object to be polished is also important. This is becausethe object to be polished is to be washed after polishing and if theadhesive property of the abrasive particles is high, the abrasiveparticles remain on the surface of the object to be polished afterwashing. Hence, the remaining abrasive particles may sometimes becomecauses of scratches in handling thereafter. Further, if the object to bepolished is a substrate for a hard disk, the existence of the remainingparticles becomes causes of deterioration of the smoothness in the casewhere a magnetic material is vaporized and deposited after polishing.

[0007] As the measures to satisfy such various requirements, in terms ofthe improvement of the polishing properties, in addition to improvementsof an abrasive, various amendments of additives to a slurry, an abrasivepad, a polishing apparatus and the like have been performed. However, interms of the improvement of the dispersibility and the adhesiveproperty, in many cases, additives have been employed to meet such arequirement based on their functions, yet any satisfactorycountermeasures to satisfy the requirement for the improvement of theabrasive particles themselves have not been proposed and no abrasiveparticle excellent both in the polishing properties and thedispersibility has been proposed. Especially, regarding the cerium-basedabrasive, abrasive particles with an extremely small particle diameterof 1 μm or smaller, further 0.5 μm or smaller, have been employed inorder to realize highly excellent surface smoothness and specularproperty, whereas it is supposed that the dispersibility and theadhesive property are deteriorated in relation to the surface energy ifthe particle diameter of particles becomes fine. However, nocountermeasures against it have not yet been performed.

[0008] The invention has been developed under the above describedsituation and aims to provide a cerium-based abrasive excellent in thepolishing capability and the polishing precision and also excellent inthe dispersibility and other properties.

DISCLOSURE OF THE INVENTION

[0009] In order to solve such problems and find a cerium-based abrasivehaving a property which abrasives are supposed to have, that is,excellent polishing capability, the inventors of the present inventionhave reviewed and made investigations into the causes of scratchesoccurring at the time of polishing. To classify the matter of thepolishing scratches, the scratches caused at the time of polishing canwidely be divided into so-called polishing scratches attributed to theexistence of coarse particles and fine scratches smaller than thepolishing scratches and caused on the final polished surface.

[0010] According to the investigation of the causes of the occurrence ofthese two types of scratches, at first, the polishing scratches areattributed to the existence of coarse particles in an abrasive slurry.The existence of the coarse particles is supposedly mainly attributed toabnormal particle growth of the small abrasive particles during aroasting step among the production steps of the abrasive particles andin addition to that, the existence is also supposedly attributed to thefact that particles with high agglomerating force in a dry state areinsufficiently dispersed when the dry particle powder is made to be anabrasive slurry after production and consequently forming coarseparticles in the slurry.

[0011] On the other hand, the cause of the occurrence of the finescratches is supposedly related to the relation between the abrasiveparticles and an object to be polished. Because an object to be polishedfor the uses for which the cerium-based abrasive is employed is, in manycases, of a different kind of materials containing silicon and aluminumas a main component. In case of polishing such a different material,fine particles of the object abraded by polishing are physically andchemically adsorbed on the abrasive particles and partially converged.The abrasive particles to which fine particles of the object areadsorbed abnormally agglomerate and the resulting agglomerates abradethe object again, resulting in the occurrence of the scratches.

[0012] Based on the above-described considerations, in order to obtain acerium-based abrasive with high precision and causing no scratch, it isrequired to prevent abnormal particle growth in the production steps.Further, in addition to that, it is also required for the abrasive toreduce agglomerating force in a dry state and high dispersibility in adispersion medium and to be kept in a dispersed state without causingabnormal agglomeration owing to the adsorption of the particles of theobject to be polished. This means that an abrasive with excellentpolishing properties is excellent in dispersibility.

[0013] Further, based on the results of the enthusiastic investigations,the inventors of the present invention come to have the conception thatcoating of the surface of abrasive particles with a silicon component oran aluminum component may be effective as a measure to reduce theagglomerating force of the abrasive particles in a dry state and achievethe present invention. That is, the invention is a cerium-based abrasivecomposed of cerium oxide as a main component, in which abrasiveparticles of the cerium-based abrasive are coated with a coating layercontaining at least either one of a silicon component of silicon or aninorganic silicon compound and an aluminum component of aluminum or aninorganic aluminum compound.

[0014] In the invention, the coating with a silicon component or analuminum component means a coating not so easily desorbed from thesurface of the abrasive particles and existing evenly on the particlesurface because the silicon component or the aluminum component is notonly physically mixed with or adhering to the abrasive particles butalso has a certain chemical bond with them.

[0015] Further, in the invention, the coating layer on the particlesurface may be a single layer in which both components, the siliconcomponent and the aluminum component, are mixed, and may be of a doublelayer structure with a combination of a layer of the silicon componentand a layer of the aluminum component. In the case where the coatinglayer forms the double coating layer structure, the lower layer and theupper layer may be respectively of the silicon component and thealuminum component or the lower layer and the upper layer may berespectively of the aluminum component and the silicon component, andthey may properly be selected depending on the material of an object tobe polished and the polishing conditions.

[0016] The cerium-based abrasive according to the invention has a weakagglomerating force in a dry state and is excellent in thedispersibility in a dispersion medium. At the same time, it scarcelycauses abnormal agglomeration attributed to adsorption of fine particlesof the object at the time of polishing. The reason why such propertiesare provided by the coating of the surface of the particles of thecerium-based abrasive with the silicon component or the aluminumcomponent is not necessarily manifest, however inventors of theinvention think that the coating layer on the surface of the abrasiveparticles takes a role like a spacer to decrease the agglomerating forcein a dry state.

[0017] Further, the abrasive with such a coating is prevented from theabnormal particle growth at the time of roasting if the coating isformed before the roasting and therefore the abrasive is free fromcoarse particles. The effect to prevent the abnormal particle growth isalso supposedly attributed to the role like a spacer of the coatinglayer and consequently, existence of the coarse particles in theproduced abrasive can be suppressed to obtain an abrasive havingexcellent polishing properties.

[0018] Moreover, owing to the function like a spacer of the coatinglayer, the cerium-based abrasive according to the invention is providedwith an effect to decrease the adhesive property to the object to bepolished. That is, the abrasive particles of the cerium-based abrasiveaccording to the invention can be desorbed from the surface of theobject without remaining by washing after polishing. The cerium-basedabrasive with low adhesive property according to the invention has noprobability of causing scratches after polishing and is capable ofreliably providing smoothness of a product.

[0019] The content of the silicon component or the aluminum componentcontained in the coating layer is desirably 0.01 to 5% by weight intotal of silicon element and aluminum element to the weight of theabrasive particles.

[0020] The range is preferably 0.05 to 3% by weight, more preferably 0.1to 2% by weight. If less than 0.01% by weight, no effect expected in theinvention can be obtained, and if more than 5% by weight, althougheffects of preventing sintering and of improving the dispersibility areprovided, uniform coating treatment becomes difficult and thus thecoating component is present alone other than on the surface of theparticles of the cerium-based abrasive, which may adversely affectpolishing evaluation.

[0021] The atomic content ratio (Si/Al) of both components in the casewhere both silicon component and aluminum component are added to thecoating layer is preferably 0.1 to 10, more preferably 0.5 to 5, in thecase where the coating layer is a single layer. On the other hand, inthe case of the double layer structure, the atomic ratio of Si/Al as theratio of the layer of the silicon component and the layer of thealuminum component composing the coating layer is preferably 0.1 to 10,more preferably 0.3 to 3. Further, in either case, it is preferable thatthe coating quantity of aluminum atom is equal to or more than thecoating quantity of silicon atom in order to prevent sintering and toimprove the dispersibility.

[0022] Detailed investigations into the cerium-based abrasive coatedwith the coating on the surface which inventors of the invention haveconducted and clarified that the abrasive particles of the cerium-basedabrasive have a small angle of repose. From that finding, the powder ofthe cerium-based abrasive according to the invention is supposed to beexcellent in the fluidity as well. It has advantages that clogging ofthe pipes in the case of pneumatic transportation is suppressed andadhering to and bridging in a storage hopper are prevented. Further,adhesion of the powder to a classifying apparatus can be suppressed byforming the coating layer before a classifying step to improve theclassification efficiency. Incidentally, in the invention, the angle ofrepose of the powder is preferably small and desirably 60 degrees orsmaller. Further, the value is preferably 55 degrees or smaller, morepreferably 50 degrees or smaller. Although the angle of repose differsdepending on the thickness of the coating layer, the angle of reposebecomes 60 degrees if the total content of silicon element and aluminumelement is 0.01% by weight to the weight of the abrasive particles andit becomes smaller as the total content increases more and becomes 50degrees or smaller if the total content is 5% by weight.

[0023] Further, the cerium-based abrasive according to the invention hasexcellent dispersibility and fluidity by itself as described above andis provided with specified characteristics by being subjected to surfacetreatment. For example, the abrasive according to the invention isprovided with water-repelling property by adding a fatty acid treatingagent such as oleic acid, stearic acid and a treating agent such assilicon oil, an organic fluorine compound. Further, fluidity can beimproved with a fluidizing agent containing a silicon-based or afluorine-based compound, and in addition the charging property and thedispersibility in wet state can be adjusted by proper surface treatingagents. In case of attaching importance to the fluidity, thecerium-based abrasive according to the invention has desirably acoupling treatment agent layer produced from a coupling agent on thesurface of the coating layer. This is because a coupling agent is richin the reactivity with hydroxyl group and a coupling agent is the mostsuitable among surface treatment agents to treat a hydroxyl group whichis supposed to exist in a large quantity on the surface of the abrasiveof the invention bearing a coating layer containing the siliconcomponent or the aluminum component as compared with a hydroxyl groupexisting on the abrasive surface having no coating layer. Formation ofsuch a coupling treatment agent layer can lower the angle of repose,resulting in an abrasive with excellent fluidity. Examples of thecoupling agent capable of forming the coupling treatment agent layerinclude a silane coupling agent, an aluminum coupling agent, a zirconiacoupling agent, and a titanate coupling agent and the layer may beformed using at least one kind of these coupling agents. This is becausethese coupling agents have high reactivity to hydroxyl group and havebeen used as an additive to improve the fluidity and the lubricatingproperty of a powder. The cerium-based abrasive particles according tothe invention coated with a layer formed using, for example, a silanecoupling agent have a smaller angle of repose by at least 5 degree thanones bearing only a coating layer.

[0024] Incidentally, the particle diameter of the particles of thecerium-based abrasive bearing the coating layer on the particle surfaceis not particularly restricted, but the average particle diameter ispreferably 0.1 to 10 μm, more preferably 0.2 to 5 μm by micro-trackmeasurement. If the value is smaller than 0.1 μm, a practical polishingspeed is hard to obtain, and if higher than 10 μm, a large number ofpolishing scratches are caused and such an abrasive cannot be employedfor precision polishing.

[0025] The cerium-based abrasive in the invention means not only theparticles themselves but also a powder of the particle agglomerates.Further, the abrasive slurry containing the cerium-based abrasiveparticles can be prepared by dispersing the abrasive as a medium to bedispersed in a dispersion medium and regarding additives having adispersing function and a cleaning function to the dispersion medium,well-known substances may optionally be employed.

[0026] Further, in the case where the cerium-based abrasive bearing thecoating containing the silicon component and the aluminum component onthe particle surface is used to produce a cerium-based abrasive slurry,a dispersion slurry using water as the dispersion medium is preferablythe abrasive slurry. Further, it is also optional to produce a slurrycontaining a variety of additives such as a dispersing agent and asurfactant in combination based on the purposes for polishing.

[0027] As described above,. the cerium-based abrasive according to theinvention has excellent polishing properties while keeping excellentdispersibility and the fluidity and is suitable as an abrasive forpolishing various glass materials. Also, the cerium-based abrasiveaccording to the invention contains the silicon component and thealuminum component on the surface and these components have chargingproperties to be respectively negative and positive. Further, thecerium-based abrasive according to the invention is easy tosurface-treat and therefore, the charging property is also adjustable.Consequently, the cerium-based abrasive according to the invention canbe used as an additive for a developer for electrostatic latent imagedevelopment to be used for the electrophotography as well as generalglass polishing. For example, in a development apparatus for which anamorphous silicon is employed as a photosensitive conductor, addition ofthe cerium-based abrasive according to the invention to a developerkeeps the surface of the photosensitive conductor clean and improves thedevelopment properties such as stability of the image density.

[0028] Further, the cerium-based abrasive according to the invention isprovided with a prolonged life by the coating and such tendency isparticularly prominent for those bearing the coating containing thealuminum component.

[0029] Next, the production method of the cerium-based abrasiveaccording to the invention, that is, a method for forming the coatinglayer on the abrasive particles will be described. As a method forcoating the abrasive particles with the silicon component and thealuminum component, a dry type coating treatment may be carried out, inother words, the cerium-based abrasive as a raw material powder beforeroasting or the cerium-based abrasive powder after roasting is mixedwith a fine powder of colloidal silica, colloidal alumina, and the like.

[0030] In this case, the average particle diameter (D50) of silicon, asilicon compound, aluminum, or an aluminum compound is properly notlarger than ⅓, preferably not larger than ⅕, and further preferably notlarger than {fraction (1/10)} of that of the cerium-based abrasive as araw material powder before roasting or the cerium-based abrasive powderafter roasting. This is because if it exceeds ⅓, mixing state, ratherthan coating, will take place and it becomes impossible to sufficientlycoat the abrasive particles.

[0031] Incidentally, in case of carrying out coating treatment for thecerium-based abrasive powder after roasting, it is preferable to carryout heating treatment at a temperature not lower than 200° C. and nothigher than the roasting temperature after the raw material powder ismixed with colloidal silica and the like. The heating treatment iscarried out because no complete coating can be formed only by simplymixing the abrasive powder with the colloidal silica and the like andthe silicon component and the aluminum component are consequentlydropped off. The heating treatment temperature is controlled to be notlower than 200° C. in order to prevent the silicon component and thealuminum component from dropping off. On the other hand, the heatingtreatment temperature is controlled to be not higher than the roastingtemperature in order to suppress the proceeding of sintering of theabrasive particles.

[0032] Meanwhile, as the method for forming an even and firm coatinglayer, a method preferably comprises steps of producing a slurry bywet-dispersing the cerium-based abrasive in a dispersion medium andadding a treatment solution containing at least either one of a siliconcompound and an aluminum compound to be slurry. Consequently, thesurface of the cerium-based abrasive particles is easily and evenlycoated with the silicon component and the aluminum component and at thesame time, the formed coating layer is firm enough to eliminate droppingof these components during use.

[0033] The coating layer formed on the surface of the abrasive particlesin the invention has effects not only to suppress the agglomeration in adry state but also to suppress the abnormal particle growth at the timeof roasting. Consequently, in order to obtain the cerium-based abrasiveexcellent in the polishing properties, it is preferable to form thecoating layer on a previously pulverized raw material and subject theresulting raw material to common treatment steps to obtain the abrasive,instead of coating treatment carried out for the completed cerium-basedabrasive. That is, in a common production method comprising a slurryproduction step of producing a slurry by mixing the abrasive rawmaterial with a dispersion medium to obtain a slurry of the abrasive rawmaterial, a pulverization step of wet-pulverizing the slurry, a roastingstep of roasting the abrasive raw material after pulverization, and aclassification step of classifying the roasted abrasive raw materialafter the raw material is dry-pulverized, it is preferable to carry outthe coating treatment by adding a treatment solution containing eitherone of the silicon compound and the aluminum compound to the slurryduring the pulverization step or after the pulverization step.

[0034] In this case, as the dispersion medium to make a slurry of theabrasive particles or the abrasive raw material at the time of carryingout the coating treatment, although organic solvents such as alcoholsand hydrocarbon-based solvents can be employed, it is preferable to usewater as a main component for the dispersion medium in consideration ofthe possible problems such as ignition in terms of work safety. Theconcentration of the abrasive or the raw material in the slurry ispreferably within a range of 5 to 50% by weight to carry out thetreatment. This is because if the concentration is lower than 5% byweight, the slurry is too thin, resulting in a decrease of theproductivity, and if the concentration is higher than 50% by weight, theviscosity of the slurry is increased and the slurry becomes difficult tostir and therefore uniform coating treatment possibly becomes difficult.Especially, in case of carrying out surface treatment for thecerium-based abrasive after classification, by controlling the slurryconcentration in the above-described range, the slurry after the surfacetreatment can conveniently be employed as a slurry for polishing as itis. Further, as a method for making the abrasive or the raw material bea slurry, the powder-state or cake-like abrasive or raw material isre-pulped with the dispersion medium to be a slurry and based onnecessity, an apparatus such as a stirring apparatus, an ultrasonicdispersing apparatus, a homogenizer, a homomixer and the like isemployed.

[0035] On the other hand, as the silicon compound and the aluminumcompound to be added to the abrasive or the raw material in the slurrystate, powders of fine particles of such as colloidal silica andcolloidal alumina may be added as they are or being made to be a slurry,however in this case also, coated fine particles may be dropped off oruniform coating cannot be formed. Consequently, regarding the compoundto be added, it is preferable to use compounds soluble in the abrasiveslurry. Especially, as described above, water is preferably the maincomponent as the dispersion medium in the invention and for that, thesilicon component and the aluminum component to be added in this caseare desirably water-soluble. As the water-soluble silicon component,sodium silicate, potassium silicate and the like are usable and as thewater-soluble aluminum component, aluminum sulfate, aluminum chloride,sodium aluminate and the like are usable. Also, in case of adding thesilicon compound and the like before the roasting step, an organiccompound for the silicon component and the like is usable if it can beconverted into an inorganic compound by roasting.

[0036] In the invention, in order to evenly and firmly coat the surfaceof the abrasive particles or the abrasive raw material with the siliconcomponent and the aluminum component, pH is preferably adjusted duringaddition or after addition of the silicon component and the aluminumcomponent to the abrasive slurry. The pH is preferably adjusted within arange of 2 to 10. This is because at pH out of the pH range, the siliconcomponent and the aluminum component of the coating on the surface ofthe particles are dissolved to give no sufficient effect of the coating.Execution of the pH adjustment makes it possible to form an even andfirm coating of the silicon component and the aluminum component ascompared with the case of simply physically mixing them.

[0037] As the pH adjustment method, during the addition or after theaddition of the silicon component and the aluminum component to theslurry, aqueous acidic and alkaline solutions may be added so as to keeppH in a prescribed range. In this case, the addition speed of thesilicon component and the aluminum component is not particularlyrestricted and they may be added evenly in the entire slurry while beingstirred. Further, five minutes or longer is sufficient for the time tokeep the pH of the slurry after addition.

[0038] In case of previously forming the coating layer on the rawmaterial in the pulverization step, the raw material slurry after thetreatment is subjected to filtering, washing, drying, roasting,pulverizing, and classifying steps by common methods to obtain a powderof the cerium-based abrasive particles. The roasting temperature at thattime is 700 to 1,200° C. and the retention time is 30 minutes to 24hours. The classification may be carried out for removing particles witha particle diameter of 10 μm or larger. Further, in order to preventdamages on the surface coating layer by carbonic acid gas evolved in theinside by the roasting carried out after the surface treatment, as thepowder to be coated, rare earth oxides are preferable rather than rareearth carbonates and more practically, the content of the volatilecomponents such as carbonic acid gas and the like at the roastingtemperature is not more than 25% by weight relative to the entire weightof the powder of the abrasive particles before coating.

[0039] On the other hand, as the method for forming a coupling treatmentagent layer on the cerium-based abrasive bearing the coating layerproduced by the above-described method, the cerium-based abrasiveproduced by the above-described method is mixed with a coupling agentand heated to cause the coupling reaction. The mixing of thecerium-based abrasive with the coupling agent may be carried out by amixer by adding the coupling agent to the cerium-based abrasive inpowder state and also by dispersing the cerium-based abrasive in wateror an organic solvent to obtain a slurry and adding the coupling agentto the obtained slurry. The mixing amount of the coupling agent ispreferably 0.1 to 5% by weight in relation to the weight of thecerium-based abrasive. This is because if it is less than 0.1% byweight, the treatment effect on the abrasive is slight and if it ishigher than 5% by weight, the coupling treatment agent layer becomes toothick and therefore the coupling component is easy to drop off andchanges the properties of the abrasive slurry during polishing.

[0040] As the coupling agent to be employed for the treatment, usableexamples are a silane coupling agent, an aluminum coupling agent, azirconia coupling agent, a titanate coupling agent, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] Hereinafter, together with Comparative Examples, preferredembodiments of the present invention will be described.

[0042] First Embodiment

[0043] A bastnasite-based cerium oxide raw material was used and loadedtogether with water into an attriter (manufactured by Mitsui Mining Co.,Ltd.) and pulverized to have the average particle diameter of 0.3 μm bya particle diameter measurement method which will be described later.After the slurry was transported to a receiving tank equipped with astirring apparatus from the attriter, an aqueous sodium silicatesolution measured so as to contain silicon in 1% by weight in relationto the cerium oxide weight was added while being stirred. After theresulting slurry was stirred for 5 minutes after addition, the pH wasadjusted to be 8 by a diluted sulfuric acid and controlled to keep thepH for 30 minutes. The obtained slurry was filtered, dried, roasted at950° C. and pulverized and then the particles with a particle diameterof 10 μm or larger were removed to obtain a powder of the cerium-basedabrasive particles. The quantity of the silicon component coating on thesurface of the particles was measured by the following method and thenthe particle size measurement and the dispersibility test were carriedout and a glass material was polished to evaluate the polishingproperties.

[0044] <Particle Diameter Measurement>

[0045] A powder of the abrasive particles in amount of 0.1 g was put in100 ml of an aqueous solution of 0.1% by weight of sodiumhexametaphosphate and dispersed for 10 minutes at 300 W by an ultrasonichomogenizer (MODEL US-300T, manufactured by Nippon Seiki ManufacturingCo., Ltd.). Some of the resulting dispersion solution was sampled andthe particle size distribution was measured by micro-track (Micro-TrackMK-II, particle size analyzer SPA MODEL 7997-20, manufactured by NikkisoCo., Ltd.). Based on the obtained data, the particle diameter value (μm)of 50% in the volumetric particle size distribution degree from thesmall particle diameter side was defined as the average particlediameter.

[0046] <Component Measurement of the Coating Layer>

[0047] A powder of abrasive particles in amount of 1 g was added to 100ml of an aqueous solution of 1 mol/l of NaOH and stirred for 4 hours bya magnetic stirrer while being kept at 50° C. temperature. The obtainedslurry was filtered by filtration paper to separate a powder and thesolution was diluted to 200 ml with pure water and the silicon andaluminum contents were quantitatively measured by ICP and conversioncalculation was carried out based on the initial weight of the powder ofthe abrasive particles to quantitatively measure the amounts of thesilicon component and the aluminum component in the coating layer.

[0048] <Dispersibility Test>

[0049] A powder of abrasive particles in amount of 0.1 g was added to100 ml of pure water and dispersed by an ultrasonic homogenizer whilechanging the time to be 1 minute, 2 minutes and so forth and the timetaken to obtain the particle diameter value of 10 μm or smaller(micro-track) for 90% in the volumetric particle size distributiondegree from the small particle diameter side was defined as the neededdispersion time. Consequently, if the needed dispersion time was short,the abrasive was judged to be excellent in dispersibility.

[0050] <Polishing Test>

[0051] Employing an Oscar type polishing tester (HSP-21 Model,manufactured by Taito Seiki Co., Ltd.) as the testing apparatus andusing a polishing pad made of a polyurethane and glass for a flat panelof 60 mm φ as an object to be polished, polishing was carried out for 5minutes by supplying a slurry of 10% by weight of the abrasive producedby mixing the above-described abrasive and pure water at a speed of 500ml/minute while setting the pressure to the face to the polished at 500g/cm² and the rotation speed of the polishing apparatus at 1,100 rpm.The glass after the polishing was washed with flowing pure water,subjected to the ultrasonic washing in pure water for one minute,further washed with flowing pure water, and dried in dust-freecondition. Incidentally, washing the glass after polishing was carriedout only with flowing water without the ultrasonic washing and theremaining amount of the abrasive particles was compared with that in thecase of carrying out the ultrasonic washing.

[0052] <Abrasive Life Test>

[0053] Further, in order to investigate the durability of an abrasive inlong time use, a life test was carried out. Using the same polishingapparatus as that for the polishing test, the life test was carried outby carrying out polishing 100 objects to be polished while circulating 5L of the slurry of 10% by weight of the abrasive and the polishingvalues for the first object, the 20th object, the 50th object, and the100th object were measured.

[0054] The evaluation by the life test was carried out for the abrasivesof the first embodiment, the second embodiment, and Comparative Example1, which will be described later.

[0055] Incidentally, to evaluate the polishing values in the polishingtest and the life test, the polishing values were calculated bymeasuring the decrease of the weight of the glass before and afterpolishing and calculating the relative values of the decrease when thedecrease of the comparative example, which will be described later, wasset to be 100. Further, regarding the existence of the scratches in thepolished surface and the existence of remaining and adhering abrasiveparticles, they were observed by a reflection method by radiating lightrays from a halogen lamp of 300,000 lux as a light source to the surfaceof the glass after polishing. Regarding the scratches, the degree andthe number of the scratches were observed and marked and evaluation wasperformed by demerit mark way on the basis of 100 points. On the otherhand, the existence of the abrasive remaining on the glass surface wasconfirmed by observing the polished face with an optical microscope.

[0056] The results of the particle size measurement, the dispersibilitymeasurement, and the polishing test are shown in Table 1. Further, theresults of the life test are shown in Table 2.

[0057] Second Embodiment

[0058] In this embodiment, a cerium-based abrasive coated with aluminumin place of silicon in the first embodiment was produced. After thebastnasite-based cerium oxide raw material was pulverized to have theaverage particle diameter of 0.3 μm in the same manner as the firstembodiment, an aqueous aluminum sulfate solution measured so as tocontain aluminum in 1% by weight in relation to the cerium oxide weightwas added to the produced slurry while being stirred. After theresulting slurry was stirred for 5 minutes after addition, the pH wasadjusted to be 6 by an aqueous NaOH solution and controlled to keep thepH for 30 minutes. The obtained slurry was filtered, dried, roasted at950° C. and pulverized and then the particles with a particle diameterof 10 μm or larger were removed to obtain a powder of the cerium-basedabrasive particles. The obtained powder of the cerium-based abrasiveparticles was evaluated in the same manner as the first embodiment andthe obtained results are shown in Table 1. Further, the results of thelife test are shown in Table 2.

[0059] Third Embodiment

[0060] In this embodiment, a cerium-based abrasive coated with bothsilicon and aluminum was produced. After the bastnasite-based ceriumoxide raw material was pulverized to have the average particle diameterof 0.3 μm in the same manner as the first embodiment, an aqueous sodiumsilicate solution measured as to contain silicon in 0.3% by weight inrelation to the cerium oxide weight and an aqueous sodium aluminatesolution measured so as to contain aluminum in 0.3% by weight were addedto the produced slurry while being stirred. After the resulting slurrywas stirred for 5 minutes after addition, the pH was adjusted to be 6 bya diluted sulfuric acid and controlled to keep the pH for 30 minutes.The obtained slurry was filtered, dried, roasted at 950° C. andpulverized and then the particles with a particle diameter of 10 μm orlarger were removed to obtain a powder of the cerium-based abrasiveparticles. The obtained powder of the cerium-based abrasive particleswas evaluated in the same manner as the first embodiment and theobtained results are shown in Table 1.

[0061] Fourth Embodiment

[0062] In this embodiment, a cerium-based abrasive coated with bothsilicon and aluminum was produced. After the bastnasite-based ceriumoxide raw material was loaded together with water into an attriter andpulverized to have the average particle diameter of 0.3 μm and afterthat, the slurry was transported to a receiving tank equipped with astirring apparatus from the attriter and then an aqueous sodium silicatesolution measured so as to contain silicon in 0.5% by weight in relationto the cerium oxide weight was added while being stirred. After theresulting slurry was stirred for 5 minutes after addition, the pH wasadjusted to be 8 by a diluted sulfuric acid and controlled to keep thepH for 30 minutes. Further, an aqueous aluminum sulfate solutionmeasured so as to contain aluminum in 0.25% by weight was added whilebeing stirred. After the resulting slurry was stirred for 5 minutesafter addition, the pH was adjusted to be 6 by a diluted sulfuric acidand controlled to keep the pH for 30 minutes. The obtained slurry wasfiltered, dried, roasted at 950° C. and pulverized and then theparticles with a particle diameter of 10 μm or larger were removed toobtain a powder of the cerium-based abrasive particles. The obtainedpowder of the cerium-based abrasive particles was evaluated in the samemanner as the first embodiment and the obtained results are shown inTable 1.

[0063] Fifth Embodiment

[0064] In this embodiment, a cerium-based abrasive coated with bothsilicon and aluminum was produced. After the bastnasite-based ceriumoxide raw material was pulverized to have the average particle diameterof 0.3 μm in the same manner as the first embodiment, an aqueousaluminum sulfate solution measured so as to contain aluminum in 0.5% byweight in relation to the cerium oxide weight was added to the slurrywhile being stirred. After the resulting slurry was stirred for 5minutes after addition, the pH was adjusted to be 6 by a dilutedsulfuric acid and controlled to keep the pH for 30 minutes. Further anaqueous sodium silicate solution measured so as to contain silicon in0.1% by weight was added while being stirred and after the resultingslurry was stirred for 5 minutes after addition, the pH was adjusted tobe 8 by a diluted sulfuric acid and controlled to keep the pH for 30minutes. The obtained slurry was filtered, dried, roasted at 950° C. andpulverized and then the particles with a particle diameter of 10 μm orlarger were removed to obtain a powder of the cerium-based abrasiveparticles. The obtained powder of the cerium-based abrasive particleswas evaluated in the same manner as the first embodiment and theobtained results are shown in Table 1.

[0065] Sixth Embodiment

[0066] In this embodiment, a cerium-based abrasive coated with silicononly was produced. After the bastnasite-based cerium oxide raw materialwas pulverized to have the average particle diameter of 0.3 μm in thesame manner as the first embodiment, an aqueous aluminum sulfatesolution measured so as to contain an aqueous sodium silicate solutionmeasured so as to contain silicon in 1.0% by weight was added whilebeing stirred and after the resulting slurry was stirred for 5 minutesafter addition, the pH was adjusted to be 8 by a diluted sulfuric acidand controlled to keep the pH for 30 minutes. The obtained slurry wasfiltered, dried, roasted at 950° C. and pulverized and then theparticles with a particle diameter of 10 μm or larger were removed toobtain a powder of the cerium-based abrasive particles. The obtainedpowder of the cerium-based abrasive particles-was evaluated in the samemanner as the first embodiment and the obtained results are shown inTable 1.

[0067] Seventh Embodiment

[0068] In this embodiment, being different from the first to the sixthembodiments, in place of the bastnasite-based cerium oxide as a rawmaterial, rare earth oxides containing 60% by weight or more of ceriumoxide in the total rare earth oxides were used to produce an abrasivewithout carrying out surface treatment at first and after that theabrasive was subjected to the surface treatment. The production steps ofthe abrasive in this case were the same as those of the first to thesixth embodiments except that the surface treatment was carried out.That is, the raw materials were loaded together with water into anattriter and pulverized, and the resulting slurry was filtered, dried,roasted at 950° C. and pulverized and then the particles with a particlediameter of 10 μm or larger were removed. The obtained powder of thecerium-based abrasive particles was dispersed in pure water so as toadjust the slurry concentration to be 10% by weight and stirred and anaqueous sodium silicate solution was added so as to control the siliconelement content to be 1% by weight in relation to the weight of theabrasive. At that time, the slurry was stirred for 30 minutes whilebeing adjusted to be pH 8 by a diluted sulfuric acid of 0.1 mol/lconcentration. After the stirring, the obtained slurry was filtered andwashed to remove sodium ion and sulfate ion and obtain a cake. The cakewas dried at 120° C. and pulverized to obtain the cerium-based abrasive.The obtained abrasive was also evaluated in the same manner as the firstembodiment and the obtained results are shown in Table 1.

[0069] Eighth Embodiment

[0070] In this embodiment, a cerium-based abrasive was produced by thesame method as the seventh embodiment and the abrasive wassurface-treated. The cerium-based abrasive was dispersed in pure waterso as to adjust the slurry concentration to be 10% by weight and stirredand an aqueous aluminum sulfate solution was added to the slurry so asto control the aluminum element content to be 1% by weight in relationto the weight of the abrasive. At that time, the pH of the slurry wasadjusted to be 8. After the surface treatment, the obtained slurry wasfiltered and washed to obtain a cake. The cake was dried at 120° C. andpulverized to obtain the cerium-based abrasive. The obtained abrasivewas also evaluated in the same manner as the first embodiment and theobtained results are shown in Table 1.

[0071] Ninth Embodiment

[0072] In this embodiment, surface treatment was carried out for acerium-based abrasive by the same method as the seventh and the eighthembodiments. The cerium-based abrasive was dispersed in pure water so asto adjust the slurry concentration to be 10% by weight and stirred andan aqueous sodium silicate solution measured so as to control thesilicon content to be 0.3% by weight in relation to the weight of theabrasive and an aqueous sodium aluminate solution measured so as tocontrol the aluminum content to be 0.3% by weight were added to theslurry while being stirred. At that time, the pH of the slurry wasadjusted to be 8. After the surface treatment, the obtained slurry wasfiltered and washed to obtain a cake and the cake was dried at 120° C.and pulverized to obtain the cerium-based abrasive. The obtainedabrasive was also evaluated in the same manner as the first embodimentand the obtained results are shown in Table 1.

[0073] Tenth Embodiment

[0074] In this embodiment, surface treatment to coat a cerium-basedabrasive with the silicon component and the aluminum component wascarried out by the same method as the ninth embodiment. In this case, anaqueous sodium silicate solution measured so as to control the siliconcontent to be 0.5% by weight in relation to the weight of the abrasiveand an aqueous sodium aluminate solution measured so as to control thealuminum content to be 0.3% by weight were added. The obtained powder ofthe cerium-based abrasive particles was also evaluated in the samemanner as the first embodiment and the obtained results are shown inTable 1.

[0075] Eleventh Embodiment

[0076] Surface treatment to coat a cerium-based abrasive with thesilicon component and the aluminum component was carried out by the samemethod as the ninth embodiment, except that an aqueous sodium silicatesolution measured so as to control the silicon content to be 0.1% byweight in relation to the weight of the abrasive and an aqueous sodiumaluminate solution measured so as to control the aluminum content to be0.5% by weight were added. The obtained powder of the cerium-basedabrasive particles was also evaluated in the same manner as the firstembodiment and the obtained results are shown in Table 1.

[0077] Twelfth Embodiment

[0078] Surface treatment to coat a cerium-based abrasive with thesilicon component was carried out by the same method as the ninthembodiment, except that an aqueous sodium silicate solution measured soas to control the silicon content to be 1.0% by weight in relation tothe weight of the abrasive was added. The obtained powder of thecerium-based abrasive particles was also evaluated in the same manner asthe first embodiment and the obtained results are shown in Table 1.

COMPARATIVE EXAMPLE 1

[0079] To be compared with the above-described first to twelfthembodiments, abrasive particles bearing no coating on the particlesurface were produced by a common method. In the same manner as thefirst embodiment, the bastnasite-based cerium oxide raw material wasused and loaded together with water into an attriter and pulverized tohave the average particle diameter of 0.3 μm measured by a particlediameter measurement method which will be described later and theobtained slurry was filtered, dried, roasted at 950° C. and pulverizedand then the particles with a particle diameter of 10 μm or larger wereremoved to obtain a powder of the cerium-based abrasive particles. Theobtained powder of the cerium-based abrasive particles was evaluated inthe same manner as the first embodiment and the obtained results areshown in Table 1. Further, the results of the life test are shown inTable 2.

COMPARATIVE EXAMPLE 2

[0080] A powder of abrasive particles was obtained in the same method asComparative Example 1 by using rare earth oxides similar to those of theseventh to twelfth embodiments as a raw material in place of the rawmaterial used in Comparative Example 1. The obtained powder of thecerium-based abrasive particles was evaluated in the same manner as thefirst embodiment and the obtained results are shown in Table 1. TABLE 1Polishing test result Existence of remaining abrasive Flowing ParticleDispersion Si, Al contents Polished Only water + ultra-sonic diametertime Si Al Polishing face flowing wave + flowing (μm) (min) (wt %) (wt%) value evalua-tion water water First 0.95 7 0.97 0 100 97 SlightlyNone embodiment existing Second 0.94 2 0 0.98 100 100 None Noneembodiment Third 0.94 4 0.29 0.30 100 99 None None embodiment Fourth0.92 5 0.49 0.24 100 98 Slightly None embodiment existing Fifth 0.97 30.09 0.49 100 100 None None embodiment Sixth 0.95 5 0.98 0 100 99Slightly None embodiment existing Seventh 1.03 5 0.94 0 102 99 SlightlyNone embodiment existing Eighth 0.99 <1 0 0.91 100 100 None Noneembodiment Ninth 0.97 3 0.27 0.27 100 99 None None embodiment Tenth 0.994 0.50 0.25 100 100 None None embodiment Eleventh 1.01 1 0.07 0.50 104100 None None embodiment Twelfth 1.06 3 0.88 0 105 99 Slightly Noneembodiment existing Comparative 1.18 >10 0 0 100 90 Existing Existingexample 1 Comparative 1.12 >10 0 0 100 92 Existing Existing example 2

[0081] TABLE 2 First object 20th object 50th object 100th object First100 93 82 63 embodiment Second 100 98 93 84 embodiment Comparative 10085 67 34 Example 1

[0082] From the above-described results, it was found that as comparedwith those for Comparative Example 1 and Comparative Example 2, thepolishing values for First to Twelfth embodiments were not decreased forthe slightly small average particle diameters. That is supposedlyattributed to the fact that sintering of fine particles is suppressed atthe time of roasting in those embodiments, resulting in small apparentaverage particle diameter. Further, regarding the evaluation results ofthe polished faces, the abrasives according to the embodiments werefound capable of providing excellent polished faces with relativelyslight scratches as compared with the abrasives of the comparativeexamples.

[0083] On the other hand, in the dispersibility test, the abrasives ofFirst to Twelfth embodiments were found capable of being dispersedwithin a short time as compared with those of the comparative examples,showing small agglomerating force among particles. Further, silicon andaluminum components were found capable of being used for surfacetreatment at a high yield ratio relative to the silicon component andthe aluminum component added by adjusting the pH at the time of surfacetreatment just like the embodiments. Especially, under the condition ofthe same addition amounts, the powder of the cerium-based abrasiveparticles coated with the aluminum component was found excellent in thedispersibility as compared with the powder of the cerium-based abrasiveparticles coated with the silicon component. Further, regarding thecleaning property after polishing, the abrasives coated with the siliconcomponent and the aluminum component of the present invention were foundexcellent as compared with surface-untreated ones.

[0084] Incidentally, in the abrasive production process of First,Second, Seventh, and Eighth embodiments and Comparative Examples 1 and2, the classification efficiency was measured to find 96%, 98%, 97%, and98% for First, Second, Seventh, and Eighth embodiments, respectively,whereas 67% and 45% for Comparative examples 1 and 2, respectively. Thisis supposedly attributed to the fact that the abnormal particle growthat the time of roasting was suppressed and also the adhesive property tothe inner walls of the pulverizer and the classifying apparatus wasdecreased owing to the formation of the coating layer for the rawmaterials of these embodiments after pulverization.

[0085] Further, regarding the life test, the abrasives of theembodiments, especially the abrasive of Second embodiment, showedrelatively high polishing value even after polishing 100th object to bepolished to make it clear that they had excellent durability.

[0086] Thirteenth Embodiment

[0087] In this embodiment, a coupling treatment agent layer was furtherformed on the cerium-based abrasive produced in First embodiment. As asilane coupling agent, γ-aminopropyltriethoxysilane was added in 0.5% byweight relative to the abrasive weight to the cerium-based abrasive andsufficiently mixed by a V-model blender and heated at 100° C. for 2hours to cause coupling reaction.

[0088] After that, the angle of repose of the resulting cerium-basedabrasive after the coupling treatment was measured to find it was 52degrees. The angle of repose of a cerium-based abrasive which was notsubjected to the coupling treatment was also measured to find it was 57degrees. Consequently, the cerium-based abrasive according to Firstembodiment was found that the angle of repose was further lowered bycarrying out coupling treatment and the fluidity could be improved.

Industrial Applicability

[0089] As described above, the cerium-based abrasive particles coatedwith the silicon component and the aluminum component according to theinvention are excellent in dispersibility and usable for polishingoptical glass lens, a glass substrate, a glass substrate for magneticrecording disks, a glass substrate for liquid crystals, a silicon-basedsemiconductor substrate or LSI, an aluminum substrate for magneticrecording disks or the like, and particularly for polishing purposes forwhich precision is required.

1. A cerium-based abrasive containing cerium oxide as a main component,wherein the abrasive particles composing the abrasive are coated with acoating layer containing at least either one of a silicon component ofsilicon or an inorganic silicon compound and an aluminum component ofaluminum or an inorganic aluminum compound.
 2. The cerium-based abrasiveaccording to claim 1, wherein said coating layer is a single layer inwhich the silicon component and the aluminum component are mixed.
 3. Thecerium-based abrasive according to claim 1, wherein said coating layerhas a double layer structure comprising a first coating layer coatingthe abrasive particles and a second coating layer coating the firstcoating layer and said first coating layer is of the silicon componentand said second coating layer is of the aluminum component.
 4. Thecerium-based abrasive according to claim 1, wherein said coating layerhas a double layer structure comprising a first coating layer coatingthe abrasive particles and a second coating layer coating the firstcoating layer and said first coating layer is of the aluminum componentand said second coating layer is of the silicon component.
 5. Thecerium-based abrasive according to any one of claim 1 to claim 4,wherein a content of the silicon component and the aluminum componentcontained in the coating layer in total weight of silicon element andaluminum element is 0.01 to 5% by weight of weight of the abrasiveparticles.
 6. The cerium-based abrasive according to any one of claim 1to claim 5, wherein said abrasive particles are provided with a couplingtreatment agent layer produced from a coupling agent further on thesurface of the coating layer.
 7. The cerium-based abrasive according toclaim 6, wherein said coupling agent forming the coupling treatmentagent layer contains at least one kind of coupling agents selected froma silane coupling agent, an aluminum coupling agent, a zirconia couplingagent, and a titanate coupling agent.
 8. A cerium-based abrasive slurrycontaining the cerium-based abrasive according to any one of claim 1 toclaim
 7. 9. A production method of the cerium-based abrasive accordingto any one of claim 1 to claim 5, wherein the production method of thecerium-based abrasive comprises the steps of producing a slurry bywet-dispersing the cerium-based abrasive in a dispersion medium andcarrying out surface treatment by adding a treatment solution containingat least either one of a silicon compound and an aluminum compound tothe slurry.
 10. The production method of the cerium-based abrasiveparticles according to claim 9, wherein said dispersion medium containswater as a main component.
 11. A production method of the cerium-basedabrasive according to any one of claim 1 to claim 5, wherein theproduction method of the cerium-based abrasive comprises a slurryproduction step of producing a slurry by mixing abrasive raw materialwith a dispersion medium, a pulverization step of wet-pulverizing theslurry, a roasting step of roasting the abrasive raw material afterpulverization, and a classification step of classifying the roastedabrasive raw material after the raw material is dry-pulverized, andduring the pulverization step or after the pulverization step, atreatment solution containing at least either one of a silicon compoundand an aluminum compound is added to the slurry to carry out surfacetreatment.
 12. The production method of the cerium-based abrasiveaccording to claim 11, wherein said dispersion medium contains water asa main component.
 13. The production method of the cerium-based abrasiveaccording to any one of claim 9 to claim 12, wherein said siliconcompound and said aluminum compound contained in the treatment solutionare water soluble.
 14. The production method of the cerium-basedabrasive according to any one of claim 9 to claim 13, wherein saidtreatment solution is added so as to adjust a total content of thesilicon element and the aluminum element at 0.01 to 5% by weight to thecerium-based abrasive or the abrasive raw material in the slurry. 15.The production method of the cerium-based abrasive according to any oneof claim 9 to claim 14, wherein the pH of the slurry is adjusted to bewithin a range of 2 to 10 after addition of the treatment solution tocarry out the surface treatment.
 16. A production method of acerium-based abrasive according to either claim 6 or claim 7, comprisingthe steps of mixing the cerium-based abrasive produced by the methodaccording to any one of claim 9 to claim 15 with a coupling agent andheating them.
 17. The production method of a cerium-based abrasiveaccording to claim 16, wherein the cerium-based abrasive is dispersed inwater or an organic solvent to produce a slurry and a coupling agent isadded to and mixed with the slurry.
 18. The production method of acerium-based abrasive according to either claim 16 or claim 17, whereinsaid coupling agent is mixed in a ratio of 0.1 to 5% by weight to theweight of the cerium-based abrasive.
 19. The production method of acerium-based abrasive according to any one of claim 16 to claim 18,wherein said coupling agent contains at least one kind of coupling agentselected from a silane coupling agent, an aluminum coupling agent, azirconia coupling agent, and a titanate coupling agent.